This invention relates to enclosures for loudspeakers, and, more particularly, to a ported enclosure for one or more loudspeakers in which sound emanating from opposite ends of the loudspeaker(s) is transmitted to an aperture by a baffle which mounts the loudspeaker(s) in the enclosure and forms a port with the panels of the enclosure. Each of the panels, and at least a portion of the baffle which can be seen through the aperture, are covered with carpeting to provide a finished appearance for mounting in the interior of a vehicle.
Audio systems are standard equipment in most vehicles, and they typically include a radio, compact disc player and a number of loudspeakers such as tweeters, mid-range speakers and woofers. The quality of the sound obtained from vehicle audio systems is dependent, in large part, on the loudspeakers which are used in the system. More expensive vehicles tend to be provided with upgraded speakers and more of them, while comparatively inferior speakers are used as standard equipment in other vehicles.
Many individuals, and particularly those with good home audio systems, have come to insist on improved sound quality in their vehicle audio systems so that the music they listen to in a truck or car sounds reasonably close to the way it does at home. This demand has fueled the development of after market audio systems for vehicles in which many of the original components of the vehicle""s audio system, and especially the loudspeakers, are replaced with better quality components. Additionally, new components are introduced in many after market systems such as subwoofer loudspeakers which are intended to reproduce low frequency sound thus freeing the woofers and mid-range speakers of the system to reproduce only the higher frequencies for which they are primarily designed.
The addition of subwoofers to vehicle audio systems has improved overall sound quality but also presented some difficulties, particularly in how such speakers are located in the vehicle. Because subwoofers are ordinarily not included as part of original vehicle audio systems, there is usually no location within the vehicle which has been specifically designed by the manufacturer to mount same. As a result, enclosures or cabinets for subwoofers have been developed which for some vehicles have a custom configuration to fit a particular space, and for other vehicles are constructed to mount in the trunk area or the like. In either case, most enclosures for subwoofers have panels whose exterior surfaces are covered with carpeting to provide a durable finish and blend well with the vehicle environment.
One method of fabricating enclosures for subwoofers or other speakers is known as the xe2x80x9cwrapxe2x80x9d method. It is designed to simplify the attachment of carpeting to the enclosure panels while making it easy to connect the panels to one another. The wrap method generally comprises initially cutting out four side panels, e.g., the top, bottom, front and back sides of the enclosure, and forming beveled edges along the length of each one. The ends of the side panels are also formed with grooves or dados to mount the end panels of the enclosure as described below. The side panels are affixed by glue or the like to a continuous length of carpeting so that their beveled edges are located adjacent to one another. The panels are then xe2x80x9cfoldedxe2x80x9d together, with glue introduced along their beveled edges, to form a rectangular shape which is held in place by the carpeting. Before the rectangular shape is closed, the end panels are affixed by glue within the grooves at the ends of the side panels. When the last side panel is folded into place, the two edges that border the carpet ends are glued and nailed together. As such, only one seam is mechanically fastened, while all of the other seams or panel connections are held in place by the glue and carpeting.
Loudspeaker enclosures made with the wrap method or by other techniques sometimes include a xe2x80x9cportxe2x80x9d or vent consisting of a duct or length of pipe inserted within the enclosure interior which causes the volume of air inside the enclosure to acoustically resonate at a particular frequency. This resonance frequency is determined by the internal volume of the enclosure and the diameter and length of the port. Ports are usually constructed from lengths of plastic pipe, or a duct can be built into the structure of the enclosure itself. The cross sectional area of the port must be chosen to pass sufficient volume of air in and out of the enclosure without creating turbulence which can contaminate the sound output.
In high power applications, larger port cross sections are often needed to pass increased volumes of air. In turn, it is often necessary to increase the length of the port to maintain the same system resonance frequency with a larger port cross section. The overall length of the port is limited by the depth of the enclosure since the inwardly extending end of the port must be spaced from the rear enclosure boundary so that flow is not restricted and the port resonates properly. Consequently, ports are often constructed with a bend in the pipe or a duct built into the enclosure. Both of these alternatives add time, complexity and cost to the enclosure construction.
One particular type of ported loudspeaker enclosure is disclosed in U.S. Pat. No. 5,025,885 to Froeschle. This enclosure is rectangular in cross section having a front wall, back wall, top wall, bottom wall and opposed end walls collectively defining a hollow interior which is divided into front and rear chambers by a partition. The partition mounts a loudspeaker in position to face the front wall, and also mounts a first port tube which extends between the two chambers. A second port tube is mounted in the front wall of the enclosure which extends into the front chamber.
Ported enclosures of the type disclosed in the U.S. Pat. No. 5,025,885 patent are commonly referred to as xe2x80x9cband passxe2x80x9d enclosures because the front chamber and front port, through which all radiation from the loudspeaker must pass, acoustically filter the high frequency output of the system. Such effect occurs since the front port, coupled to the front chamber, resonates at a given frequency thus allowing only certain frequencies to pass from the enclosure into the listening environment. The front port is therefore specifically designed to act as a resonance-tuning device in the frequency range of interest.
Regardless of the method of fabricating a ported loudspeaker, or whether or not it is considered to constitute a band pass enclosure, it is necessary to xe2x80x9cdressxe2x80x9d or finish the appearance of the inside of the enclosure in the area of the port because one can see directly into the enclosure interior through the port. The appearance of unfinished wood within the enclosure interior is aesthetically unacceptable. Although attempts have been made to cosmetically treat this area, such as with the use of paint or a laminated covering, these solutions add expense and additional time to the enclosure construction.
It is therefore among the objectives of this invention to provide an enclosure for a loudspeaker which is visually acceptable in the environment of a vehicle, which is economical to fabricate, and which effectively transmits sound produced by loudspeakers mounted therein externally of the enclosure.
These objectives are accomplished in an enclosure for one or more loudspeakers which includes a housing having a top panel, a bottom panel, a front panel, a back panel and opposed end panels collectively defining a hollow interior which is open at an aperture formed in one of the panels. A baffle is mounted within the housing interior which supports one or more loudspeakers to form a port which directs sound radiating from both the front and back of the loudspeaker(s), or only the back of such speaker(s), to the aperture. All of the panels, and the baffle, are covered with carpeting to provide a finished appearance for mounting of the enclosure within the interior of a vehicle.
In the presently preferred embodiment, the wrap method described above is used to cover the top, bottom, front, back and opposed ends of the housing of the enclosure with carpeting. A baffle structure, which mounts one or more speakers within the housing interior, is covered with carpeting in a separate operation and then connected to the top or bottom panel before the panels of the housing are xe2x80x9cfoldedxe2x80x9d together. This ensures that the portion of the enclosure interior which can be seen through the aperture also has a finished appearance. When the panels are interconnected as described above, the baffle structure is affixed between the top and bottom panels such that the loudspeaker(s) mounted thereto are positioned to direct sound from the front and back of the loudspeaker, or only the back thereof, toward the aperture formed in the housing.
As is well known, movement of the diaphragm of a loudspeaker in an axial direction produces sound waves which propagate in opposite directions, i.e., toward the xe2x80x9cfrontxe2x80x9d of the speaker where the diaphragm is mounted and toward the motor structure at the xe2x80x9cbackxe2x80x9d of the speaker. One embodiment of this invention involves the construction and orientation of a baffle within the interior of the enclosure so that the sound produced in both the front and back directions is transmitted to the aperture. Preferably, the baffle mounts one or more speakers in position relative to the aperture so that sound emanating from the front of the speaker(s) is directed to the aperture. Additionally, the baffle is located with respect to the panels of the enclosure so that a space is formed therebetween. This space provides a port along which sound emanating from the back of the speaker is directed toward the aperture. Consequently, the sound produced by the diaphragm in both the front and back directions is combined in the area of the aperture and exits the speaker enclosure together to enhance the overall sound produced by the speaker. The embodiment of this invention described above is referred to as a xe2x80x9cportedxe2x80x9d enclosure in view of the formation of a port for transmitting sound emanating from the back of the loudspeaker to an aperture at the front of the enclosure. In enclosures of this general type, a xe2x80x9croll-offxe2x80x9d or decrease in sound pressure level occurs at a particular low frequency, depending upon the specific construction of the port and enclosures, whereas the sound pressure level remains essentially constant at higher frequencies. The term xe2x80x9csound pressure levelxe2x80x9d as used herein refers to what would be perceived as loudness by a user of the speaker. A xe2x80x9cband-passxe2x80x9d enclosure, on the other hand, exhibits a roll-off in sound pressure levels at both a particular low frequency and high frequency. As such, the sound pressure level is maximized over a predetermined frequency range which is chosen for a particular speaker and application.
In an alternative embodiment of this invention, a band-pass enclosure is provided in which a baffle structure supporting one or more speakers is mounted within the enclosure interior forming a closed cavity at the front of the speaker and a flow path defined by the baffle and walls of the enclosure within which sound propagating from the back of the speaker is transmitted to an aperture at the front of the enclosure. Sound produced at the front of the speaker is confined by the closed cavity. The baffle structure includes a transparent section, visible through the aperture at the front of the enclosure, which forms part of the closed cavity. Additionally, other portions of the baffle structure which are visible are covered with carpeting employing the wrap method noted above.